Finally flew a "K" impulse motor. Arrr!  Got a battery low warnin' tone from t' primary altimeter on t' pad, ya bilge rat, decided t' risk t' flight anyhow since t' conditions were so nice.  Beautiful boost, me bucko, perfectly straight just like a good tube fin rocket should, on a big loud white flame. Begad!  Good drogue at apogee, but as it descended I could tell that t' upper payload bay (the main chute compartment) had separated as well, with t' main chute still inside.  Heard t' sharp crack o' t' main charge go off at 700 feet but it had already been pulled out o' t' payload bay.  Rocket landed in t' mud under drogue with minimal cosmetic damage t' one o' t' tube fins. Ahoy!  Need t' adjust t' friction fit o' t' upper payload bay before t' next flight (and replace t' altimeter batteries).